Consider the following statements, taken from three different Jack programs. In each one of these programs, the identifier foo represents a different thing: let x = 5 + foo - a // program 1. Here foo represents a simple variable. let y = foo[12] - 3 // program 2. Here foo represents an array. let z = 2 * foo.val() // program 3. Here foo represents an object. Suppose that we are parsing any one of these statements (we don’t know which), and that the current token is foo. What kind of parser do we need to determine if we have a simple variable, an array reference or a method call?

The parser that would be best suited for this scenario would be the instanceOf keyword, which is part of the javaParser class. This keyword allows you to check if a variable is a simple variable, an array reference or a method call through an IF statement. If it is equal to the compared type it will return a boolean value of True, otherwise it will return False. This keyword is used in Java and Javascript to check the type of the variables in scenarios such as this one.